1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a technique which is effectively applicable to a liquid crystal display device which includes a silicon nitride film.
2. Description of Related Art
An active matrix liquid crystal display device forms a holding capacitance in the inside of a pixel for holding a video signal written in the pixel for a relatively long time.
The inventors of the present invention filed a patent application (see following patent document 1) on one method for forming such a holding capacitance.
FIG. 7 is a cross-sectional view of an essential part showing one example of the holding capacitance described in patent document 1.
As shown in FIG. 7, in an IPS (In-Plane Switching) type liquid crystal display device described in patent document 1, an interlayer insulation film IN2 and an organic insulation film PAS are formed to cover a source electrode SD2 of a thin film transistor in order from below. A contact hole CH3A is formed in the interlayer insulation film IN2 and the organic insulation film PAS in a penetrating manner. A counter electrode CT and a reflection film RAL are formed on the organic insulation film PAS in order from below. Further, an interlayer insulation film IN3A is formed to cover the organic insulation film PAS, the counter electrode CT and the reflection film RAL. The interlayer insulation film IN3A is a coated insulation film or an insulation film formed by a CVD method and is formed also in the inside of the contact hole CH3A. Further, in the interlayer insulation film IN3A, a contact hole CH3B is formed more inside than the contact hole CH3A. A pixel electrode PX is formed on the interlayer insulation film IN3A. Further, the pixel electrode PX is connected with the source electrode SD2 of the thin film transistor via the contact hole CH3B and a video signal is applied to the pixel electrode PX via the thin film transistor. Liquid crystal not shown in the drawing is driven by an electric field generated between the pixel electrode PX and the counter electrode CT thus performing a display of an image.
Here, the holding capacitance is formed by the counter electrode CT (including the reflection film RAL), the interlayer insulation film IN3A and the pixel electrode PX.    Patent Document 1: Japanese patent application no. 2005-312165